The present invention relates to a technique for storing a vehicle identification code in a vehicle electronic control unit.
The vehicle identification number (VIN) code has been used as a standard for identifying vehicles. The VIN code system is specified for character strings representing the specification and options of a vehicle, a factory where the vehicle was assembled. A VIN code is unique for each vehicle for identifying the vehicle. In a vehicle, a VIN code is imprinted in various parts. Even if a vehicle is disassembled, the VIN code on each component permits that the component to be identified as a component of the specific vehicle.
The VIN code is imprinted in an electronic control unit (ECU) of a vehicle, which controls the engine. The VIN code is typically stored in a nonvolatile memory such as an electronically erasable and programmable read only memory (EEPROM) of the engine ECU during the assembly at the manufacturer (Japanese Laid-Open Patent Publications No. 2001-301572, No. 2000-185606, No. 11-255079, and No. 5-172702).
Many types of EEPROM require data to be written more than one byte at a time. Some EEPROMs cannot permit data to be written other than four, eight or sixteen bytes at a time. Since a VIN code is a seventeen digit character string, the size of the unit of data writable in an EEPROM can cause a drawback.
When writing a VIN code in an EEPROM that only permits data to be written eight bytes at a time, a memory area of twenty-four bytes, which corresponds to three sets of eight byte writing, is required. Although the VIN code is a seventeen digit character string and thus has a size of seventeen bytes, data of only sixteen bytes can be written in two writings of eight-byte data. Accordingly, to complete the writing of the data in the EEPROM, another writing process is needed. Therefore, a twenty-four byte memory area is needed in the EEPROM. At this time, seven bytes, which correspond to the difference between the written twenty-four byte data and the seventeen byte data representing the VIN code, is wastefully consumed. For the same reason, when writing a VIN code in an EEPROM that permits data to be written sixteen bytes at a time, a memory area of thirty-two bytes, which corresponds to two sets of sixteen byte writing, is required. In this case, fifteen bytes, which correspond to the difference between the written thirty-two byte data and the seventeen byte data representing the VIN code, is wastefully consumed.
The modes for reading and writing data to versatile EEPROMs are on public view. If a VIN code is written in such an EEPROM without being changed, anyone can easily reads the content of the VIN code. Therefore, the VIN code of a stolen engine ECU is easily tampered with. This creates a drawback in the antitheft measures.